The present invention relates to a current sense amplifier for sensing the current in the output stage or stages providing the phase or channel currents in a voltage converter, e.g., a multi-phase converter or power supply.
In a multi-phase converter, a number of switching power supplies, for example buck converter stages, are controlled by a power supply controller and driver stage. Each of the phase stages is coupled across a DC voltage bus and provides a portion of the output current, typically in a time phase sequence.
FIG. 1 shows a block diagram of a multi-phase converter to which the invention is applicable. FIG. 1 shows a two-phase converter, but the invention is applicable to converters having more phases.
A controller 10 provides control signals, typically pulse width modulated (PWM), to control the turn-on of the output stages 20 and 30. The first output stage 20 provides a first output phase to the output of the converter which is developed across an output capacitor C. Each converter output phase stage, here a buck converter, comprises two series connected switches, for example MOSFETS, connected in a bridge across the DC bus VIN. Each stage comprises a high side and a low side transistor which are switched complementarily with a dead time between the on times of the two switches. Typically, each stage 20 and 30 supplies output current to the output VOUT at a different time so that the currents in the inductors L1 and L2 supplied by the high side switches flow to the output at different times. In this way, each output stage contributes to the total current provided at VOUT. Multi-phase converters are typically employed in personal computers, laptops and servers, for example, and can provide very high currents, typically at low voltages of less than 2 volts required by today's modern microprocessors. As is well known, the high side switch provides current to the inductor to charge the inductor and output capacitor and power the load. When the high side switch goes off, the low side switch is turned on and continues to source the inductor current to the load. Each output stage is operated in a timed sequence so that each high side output transistor provides output current to the load at a different time.
The controller 10 in FIG. 1 also shows the CPU microprocessor load 15 which is provided with power at the output VOUT. In addition, the microprocessor provides a digital VID signal which consists of a number of bits to inform the controller 10 of the output voltage required, which can vary depending upon the CPU's operating conditions, i.e., whether it is in a high power state or a low power state. Further, the controller 10 may have additional inputs from the CPU including a signal which controls the conduction state of the output inductors L1 and L2, e.g., to a continuous conduction state; whether the controller 10 is in single or two-channel (phase) operation. Further, a thermal monitoring signal may be supplied from controller 10 to the CPU and provides thermal monitoring output to enable the CPU to monitor the temperature of the power controller 10.
In addition, the controller 10 provides a CLOCK ENABLE signal which starts the CPU system clock and a signal to initialize the CPU after a delay. In addition, controller 10 receives a signal VR-ON which enables the controller 10 and may have a connection to a serial bus, for example an SM bus, for monitoring or control by another processor.
In multi-phase converter circuits, it is necessary to sense the output current of each phase in order to regulate the current flowing through each phase to provide adaptive voltage positioning, to equalize the currents and to monitor for overcurrent conditions. This must be done accurately and reliably.